1. Field of the Invention
The present invention relates to an improvement of a picture image display apparatus and especially concerns a picture image display apparatus having a novel manner of scanning.
2. Description of the Prior Art
Three of the inventors of the present invention have invented and proposed a multiple electron beam type picture display apparatus described in the specification of the Japanese patent application Sho No. 53-106788 filed on Aug. 30, 1978 and also described in the specification of the U.S. Pat. No. 4,227,117 patented on Oct. 7, 1980. The apparatus described in the above-mentioned Japanese patent application and the U.S. Patent comprises in a flat type vacuum enclosure a row of parallelly disposed linear thermionic cathodes (i.e., line cathodes, each of which comprises a linear filament line to be heated by a low voltage, e.g., D.C. 10V and electron emissive oxide coating thereon, and hereinafter is referred to as linear thermionic cathode), electron beam forming electrodes, a row of control electrodes parallelly disposed in a direction perpendicular to those of the thermionic cathodes, a row of vertical deflection electrodes, a row of horizontal deflection electrodes, a phosphor screen formed on a face panel and an anode layer formed on the phosphor screen.
In the operation of such multiple electron beam type display apparatus described in the abovementioned specifications, scannings of beam spots on the phosphor screen are made in the known line-at-a-time type scanning, wherein an ordinary time-sequential image signal is converted into a plural number of parallel signals. For example, by taking a case to display an image field raster having numbers of picture elements of 240 (in vertical direction) times 321 (in horizontal direction), with regard to the horizontal scanning of the beam spots the raster is divided into a plural number N of vertically oblong sections, wherein the horizontal scannings are carried out parallelly in all of N sections. Then, each section has picture elements of n=321/N in the horizontal direction. For example, when the number N of the vertical sections is 107, the number n of picture element in each section is 3. For such example, 107 beam spots are produced from each linear thermionic cathode and 107 control electrodes are provided in order to control the 107 electron beam intensities. In the apparatus, the horizontal scanning is made by using a saw-tooth wave having a horizontal scanning period H applied to the horizontal deflection electrode and in a manner that all the N beam spots are deflected simultaneously to scan in the same direction taking one horizontal scanning period H. The horizontal scanning period H is equal to the horizontal scanning period of the ordinary time sequential television signal. In order for attaining such line-at-a-time-scanning, the ordinary time sequential image signal is preliminarily converted into the N parallel signals of the line-at-a-time type.
The vertical scanning of the described apparatus is made by dividing the raster into a plural number M of horizontally oblong sections, and at first in the first section, for example in the uppermost section, the plural number of beam spots, which simultaneously scan, also scan vertically (downwards). When the vertical scanning in the first section is over and all the beam spots reach the bottoms of the first horizontally oblong sections, then the forming of electron beams from the electron from the first linear thermionic cathode ends and the forming of electron beams from the electrons from the second linear thermionic cathode starts, and the vertical scannings of the beam spots start in the second horizontally oblong section and scan downwards in the same way as in the first section. The vertical scanning is made thus downwards to the bottom or M-th section by applying a saw-tooth wave having a period V/M, where V is the vertical scanning period of the ordinary television signal. For the abovementioned example of the raster having the number of vertical picture element of 240, when the number M of the horizontally oblong sections is 48, each of the section has the horizontal scanning lines of a number of m=240/48=5. That is to say, the example apparatus uses 48 linear thermionic cathodes, and each cathode vertically scans to produce 5 horizontal scanning lines.
FIG. 1 shows a block diagram of an example of the circuit for driving the abovementioned apparatus described in the abovementioned specifications. The circuit of FIG. 1 is constituted as follows. A video signal from the input terminal 12 is led to a video signal amplifier 13 and a synchronization signal separator 14, the output of which is given to a sampling pulse generator 15 and a synchronization signal generator 19. A memory circuit 16 receives a time sequential signal from the video amplifier 13 and sample-holds it in order for conversion to the parallel type video signal by a multiplexer circuit 17. That is the multiplexer circuit 17 takes out a memorized video signal from the memory 16 and rearranges it into the N (=107) parallel signals, in each of which n (=3) data in the memory 16 are rearranged into time sequential signal to take the time period of H. The parallel outputs of the multiplexer circuit 17 are given through amplifiers 18 to the control electrodes of the display apparatus. Horizontal deflection signal generator 20 and vertical deflection signal generator 22 receive a signal from the synchronization signal generator 19 and issue a horizontal deflection signal and vertical deflection signal through the amplifiers 21 and 23 to the horizontal deflection electrodes and vertical deflection electrodes of the display apparatus, respectively. A cathode control circuit 24 receives a signal from the synchronization signal generator and issues a control signal to the linear thermionic cathodes, in order that electron beams are selectively formed from the electrons from a selected linear thermionic cathodes in sequence by application of negative potential with respect to the electrode 3 thereto, thereby to scan for the period of m.times.H.
FIG. 2 shows waveforms (A), (B), (C), (D), (E), (F) and (G) of various parts of FIG. 1 circuit for the example of n=3 and m=5. The waveforms (A) and (B) are those of horizontal synchronization signal and vertical synchronization signal, wherein H shows the time period of one horizontal scanning and V shows the time period of one vertical scanning of the ordinary television signal. The waveforms (C) and (D) are voltages to be applied to the first and the second linear thermionic cathodes, respectively for switchingly operating the cathodes in sequence. The waveforms (E) and (F) are issued from the vertical deflection signal generator circuit 22 and horizontal deflection signal generator circuit 20, respectively, and the waveform (G) is the control signal to be applied to the control electrode 4 of the display apparatus. Accordingly, the scannings of the beam spots seen at enlarged parts of the phosphor screen is as shown in FIG. 10(a).
The circuit of FIG. 1 uses saw-tooth shape signals for the horizontal deflection as shown by FIG. 2 (E). The horizontal deflection electrodes comprise, for example, in the abovementioned example apparatus 107 pairs (i.e., 214 rods), of vertically oblong electrodes and hence the horizontal electrode has such a large inter-electrode capacitance of several hundred pF. Accordingly, to drive such electrodes with a large capacitance with the saw-tooth wave signal has a great difficulty of requiring such a high voltage signal of 100 to 200 volts and a considerable large power in order to ensure sufficiently short retracing period necessary for accurate horizontal scanning, and accordingly requiring such expensive circuit of emitter follower circuit or single-ended push-pull circuit.